Hyperbranched polyester having nitrogen core: synthesis and applications as metal ion extractant

REACTIVE&

Reactive & Functional Polymers 61 (2004) 255–263

www.elsevier.com/locate/react

FUNCTIONALPOLYMERS

Hyperbranched polyester having nitrogen core: synthesisand applications as metal ion extractant

Anupama Goswami, Ajai K. Singh*

Department of Chemistry, Indian Institute of Technology, New Delhi 110016, India

Received 5 April 2003; received in revised form 26 May 2004; accepted 2 June 2004

Available online 30 July 2004

Abstract

Hyperbranched polyesters, based on 2,2-bis(hydroxymethyl)propionic acid as an ABx monomer and triethanol

amine as a core molecule were synthesized and characterized with 13C{1H} NMR spectroscopy and size exclusion

chromatography. The sorption behavior of the hyperbranched polyester systems containing the oxygen ligating sites

towards ions such as Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Pb(II) and Fe(III) was studied for the first time. The effi-

ciency of binding (EOB) of the system for the seven metal ions was found to be in the range of 0.6–26.0 moles of metal

ions per mole of the polyester, indicating good potential of some of them for metal extraction. The optimum pH range

for the maximum extraction of metal ion was found to be 5.0–7.0 for Cu(II) and Pb(II), 4.5–7.0 for Fe(III), 6.0–8.0 for

Co(II) and Ni(II), 6.0–7.5 for Cd(II) and 6.5–8.0 for Zn(II). The hyperbranched polyesters were found to be fully

efficient for the extraction of these metal ions at 10 ngml�1 concentration level.

� 2004 Elsevier B.V. All rights reserved.

Keywords: Hyperbranched-polyester; Metal ion; Extraction; Sorption; Synthesis; Characterization

1. Introduction

Dendritic macromolecules due to their well

defined and unique macromolecular structure, are

attractive scaffolds for a variety of high-end ap-

plications. Their utility [1–4] has been shown in

catalysis, medicinal chemistry, magnetic reso-

nance imaging, combinatorial chemistry, light

harvesting, emission and amplification functions.

* Corresponding author. Fax: +91-11-686-20-87.

E-mail address: [email protected] (A.K.

Singh).

1381-5148/$ - see front matter � 2004 Elsevier B.V. All rights reserv

doi:10.1016/j.reactfunctpolym.2004.06.006

Like dendrimers, hyperbranched polymers are

built from ABx functional monomers giving(x� 1) potential branch points per repeat unit.

Because of the similarity in branching, hyper-

branched polymers and dendrimers have many

common features, such as improved solubility

compared to that of linear polymer of the same

molecular weight. The interest in structurally less

perfect hyperbranched polymers is also very

strong [5–11] due to the advantage of their easyand cheaper one step synthesis. In fact, when non-

perfect structure is of not much concern, they are

more suitable as their large-scale production is

ed.

mail to: [email protected]

256 A. Goswami, A.K. Singh / Reactive & Functional Polymers 61 (2004) 255–263

easier. Perstorp Polyol Inc (USA) has made

commercially available several dendritic/hyper-

branched polymers with the trade name ‘Boltorn’.

For polymer supported ultrafiltration (PSUF) [12]

which is emerging as a promising process for the

treatment of water contaminated with toxic metalions, dendrimers and hyperbranched polymers

both may be good candidates. This is because the

efficiency of PSUF is dependent on binding of

pollutant to the polymer and sorption of the

polymer onto ultrafiltration membrane. Conse-

quently, the availability of polymers with large

metal binding capacities and weak sorption ten-

dencies on membrane is critical in the develop-ment of cost effective PSUF processes. Thus

water-soluble dendrimers with chelating func-

tional groups and surface groups having weak

binding affinity toward ultrafiltration membranes

are expected to be good candidates for PSUF and

may open unprecedented opportunities in this

context. However, metal extraction by dendritic/

hyperbranched polymers has not been investi-gated, except the single report on poly(amido-

amine) (PAMAM) dendrimers, which have been

used for the extraction of Cu(II) ions from

aqueous solution by Tomalia et al. [13] and in-

volves the amino groups and tertiary nitrogen. It

was therefore thought worthwhile to design hy-

perbranched system containing oxygen-ligating

sites and explore its extraction capabilities formetal ions. To design such a system 2,2-bis(hy-

droxymethyl)propionic acid as an ABx monomer

and triethanolamine as a core molecule have been

used and the various generations of the hyper-

branched polyester have been characterized by13C NMR and size exclusion chromatography.

They contain ester and terminal hydroxyl groups

in abundance and due to high density of oxygenligating sites may be considered as a good mate-

rial for ‘hard’ metal ion extraction. Therefore,

extraction of Cu(II), Ni(II), Co(II), Pb(II), Zn(II),

Cd(II) and Fe(III) with these newly synthesized

hyperbranched polyesters has been studied. The

results of these investigations are reported in the

present paper. Hult et al. [14,15] have already

designed dendritic/hyperbranched systems similarto that of those reported but not with nitrogen as

the core.

2. Experimental

2.1. Materials

Bis-hydroxymethyl propionic acid (bis-MPA)and p-toluenesulphonic acid (p-TSA) were pro-

cured from Across Organics (New Jersey, USA)

while triethanolamine (TEA) from E. Merck

(Mumbai, India). Boltorn H30 polymer was ob-

tained from Perstorp Polyols, Inc (Ohio, USA)

They were used as received. All solvents were

distilled before use. The stock solutions of metal

ions (concentration 1000 mg l�1) were preparedfrom analytical reagent grade cadmium(II) iodide,

cobalt(II) chloride hexahydrate, copper(II) sul-

phate pentahydrate, nickel(II) sulphate hexahy-

drate, zinc(II) sulphate heptahydrate, lead(II)

nitrate and ferric chloride by dissolving their

appropriate amounts in 10 ml of concentrated

HCl or HNO3 and making up the volume to 1 l.

These solutions were standardized [16] andworking solutions of the metal ions were made by

their suitable dilution with double distilled water.

HCl (pH 1–2), 0.5 mol l�1 acetate-acetic acid

buffer (pH 3–5), 0.5 mol l�1 phosphate buffer (pH

6–7), 0.5 mol l�1 NH3–NH4Cl buffer (pH 8–10)

were used to adjust/maintain pH of the solutions,

wherever found suitable. Otherwise, dilute solu-

tions of HCl and NaOH were used for pH ad-justments. The glassware were washed with

chromic acid and soaked in 5% HNO3 for over-

night and cleaned with doubly distilled water

before use.

2.2. Instruments

13C{1H} and 1H NMR spectra were recorded

on a Bruker Spectrospin DPX 300 MHz NMR

spectrometer using DMSO-d6 as solvent. The 1H

and 13C spectra were referenced using the solvent

signal. Quantitative 13C{1H} spectra were ob-tained using the INVGATE experiments, which

suppresses the NOE effect due to decoupling of

the protons during acquisition. The recycle delay

between successive scans was 10 s. Size exclusion

chromatography (SEC) was performed on Waters

SEC system equipped with differential refrac-

tometer of Waters (Model 410) and Styragel HR1

A. Goswami, A.K. Singh / Reactive & Functional Polymers 61 (2004) 255–263 257

and HR3 columns of Waters (Water Corpora-

tion, Milford, USA). THF was used as a solvent

and linear polystyrene standards with low poly-

dispersity indices were used for calibration. Stir-

red ultrafiltration cell (Amicon Bioseparation,

Millipore Corporation, Bedford, USA) with dis-posable filter membranes (nominal weight cutoff

500 and 1000) (Amicon Bioseparation) was used

for separating metal enriched hyperbranched

polyesters. Flame atomic absorption spectrometer

of Electronic Corporation of India Limited (Hy-

derabad, India), Model 4139, equipped with air-

acetylene flame (air and acetylene flow rates 10

and 2 lmin�1 respectively) was used for metal iondetermination. The wavelengths used for moni-

toring Cd, Co, Cu, Fe, Ni, Zn and Pb are 228.8,

240.0, 324.8, 248.3, 232.0, 213.9 and 212.0 nm,

respectively.

2.3. Synthesis of hyperbranched polyesters

2.3.1. First generation (G1)

Bis-MPA (4.023 g, 30 mmol), TEA (1.49 g, 10

mmol) and p-TSA (0.020 g, 0.105 mmol) were

mixed in a three necked round bottom flask

equipped with a nitrogen inlet and a drying tube.

The flask was placed in a hot oil bath maintained

at 140 �C. The mixture was stirred using magnetic

stirrer for 1 h under a stream of nitrogen to re-

move water formed from the reaction mixture.

2.3.2. Second generation (G2)

Bis-MPA (6.030 g, 45 mmol), TEA (0.745 g, 5

mmol) and p-TSA (0.030 g, 0.158 mmol) were

mixed in a three necked round bottom flask

equipped with a nitrogen inlet and a drying tube.

The flask was placed in an oil bath, which was pre-

heated and maintained at 140 �C. The mixture wasallowed to react for 6 h with stirring on a magnetic

stirrer under a stream of nitrogen, which removed

water formed during the reaction.

The other generations of the polyester were

synthesized by a similar one step procedure except

that the precursors were taken in appropriate

stoichiometric ratio and reactions were carried out

for 10, 14 and 18 h for generations G3, G4 and G5,respectively. p-Toluene sulphonic acid was added

(0.5 wt% of bis-MPA) in all these reactions.

2.4. Synthesis of model compounds

2.4.1. Ethyl-2,2-bis(methylol)propanoate (1)Bis-MPA (5.0 g, 37 mmol) was dissolved in

ethanol (50 ml) and 0.5 ml of concentrated sul-phuric acid was added to it. The reaction mixture

was refluxed overnight. Thereafter, ethanol was

evaporated off from the mixture on a rotary

evaporator and the resulting viscous liquid residue

was treated with 20 ml of 0.1 M NaHCO3 solution.

The compound (1) was extracted into chloroform

(100 ml) from the aqueous slurry. The solvent

from the extract was also evaporated off on a ro-tary evaporator and the crude liquid product 1 was

obtained, which was purified using column chro-

matography (silica gel, hexane/ethyl acetate).

1: CH2CH3OOCCCH3(CH2OH)21H-NMR: d

(ppm) 3.99–4.06 (q, 2H, –COO–C H2–), 3.40–3.52

(m, 4H,–CH2–OH), 4.55–4.59 (t, 2H, –CH2–OH),

1.13–1.18 (t, 3H, CH3–CH2–), 1.03 (s, 3H, CH3–

C–). 13C{1H }-NMR: d (ppm) 174.7 (–COO–), 64.5(CH2–OH), 59.8 (–COO– CH2–), 49.2 (–C–), 13.3

(CH2–CH3), 16.2 (CH3).

2.4.2. Ethyl-2-methylol-2-(acetoxymethyl)propano-

ate (2) and ethyl-2,2-bis(acetoxymethyl) propano-

ate (3)Model compound 1 (0.5 g, 3.08 mmol) was

dissolved in 25 ml of dicholoromethane and acetylchloride (0.27 g, 3.39 mmol) taken in dichlorom-

ethane (10 ml) was added drop wise to it. The

mixture was stirred for 12 h. The solvent was

evaporated on a rotary evaporator to give a liquid

residue. The compounds 2 and 3 were separated

and purified from this liquid residue using column

chromatography (silica gel, hexane/ethyl acetate).

2: CH2CH3OOCCCH3(CH2OH)(CH2OO-CCH3)

1H-NMR: d (ppm) 4.02–4.15 (m, 4H, –

COO–CH2–, –CH2–CH3), 3.3 (d, 2H, –CH2–OH),

1.99 (s, 3H, –CH3–COO–), 1.14–1.18 (t, 3H, CH3–

CH2–), 1.08 (s, 3H, CH3–C–).13C{1H}–NMR: d

(ppm) 173.3 (–COO–CH2), 170.1 (–CH3–COO–),

65.1 (CH2–CH3), 63.1 (CH2–COO–), 59.9 (CH2–

OH–), 47.5 (–C–), 13.2 ( CH3–CH2), 16.3 (CH3),

19.5 (CH3–COO–).3: CH2CH3OOCCCH3(CH2OOCCH3)2

1H-

NMR: d (ppm) 4.07–4.17 (m, 6H, –COO–C

H2CH3, –CH2–OOC–CH3), 2.0 (s, 6H, –CH3–


COO–), 1.14–1.25 (m, 6H, CH3–C, CH3–CH2–)13C{1H}-NMR: d (ppm) 172.0 (–COO–CH2),

169.5 (–CH3–COO–), 64.8 (CH2–COO–), 60.4

(CH2–CH3), 45.7 (–C–), 19.8 (CH3–COO–), 16.8

(CH3–C–), 13.4 (CH3–CH2).

2.5. Procedure for metal enrichment on hyper-

branched polyesters (G2, G3, G4 and G5)

The generations from second to fifth were

studied for metal ion enrichment. The polyester

was taken as an aqueous solution and its extent of

binding (EOB) for the metal ions was determined

as a function of molar ratio of metal ion to poly-ester present in the solution as described below.

1. The polyester (0.005 g) was dissolved in 10 ml of

distilled water. The solution was mixed with a

solution (25 ml) containing one of the seven me-

tal ions, Cu(II), Pb(II), Fe(III), Co(II), Ni(II),

Cd(II) and Zn(II) (total concentration 0.1–2.0

mg) after adjusting its pH to an optimum level

(5.0–7.0, 5.0–7.0, 4.5–7.0, 6.0–8.0, 6.0–8.0, 6.0–7.5 and 6.5–8.0 respectively). The total volume

of the mixture was made to 50 ml. The solution

was stirred for 45 min on a magnetic stirrer.

2. The hyperbranched polyesters from the aque-

ous solution were separated by an ultrafiltration

cell equipped with Millipore disposable filter

with the nominal molecular weight cut-off of

500 Dalton (for G2) and 1000 Dalton (for G3,G4 and G5).

3. The metal ion concentration in the filtrate

solution (Ma) was measured by a previously

standardized flame atomic absorption spec-

H

HOH

O

O

NOH

OH

OHCH3

O

Bis- MPA TEA

+p

1

Scheme

trometer (FAAS) after suitable dilution with

double distilled water (if required).

3. Results and discussion

3.1. Synthesis of hyperbranched polyesters

The acid-catalyzed esterification procedure

(Scheme 1 for G1) used for synthesis was driven

towards high conversion by removing the water

formed continuously by passing nitrogen during

the course of reaction. In order to increase theprobability that unreacted acid groups reacted

with the hydroxyl functionality of dendritic or

hyperbranched skeleton and not with another free

monomer, the ratio of free bis-MPA to hydroxyl

groups present on polyesters was kept as low as

possible.

Therefore, bis-MPA was added in successive

portions corresponding to the stoichiometricamount for each generation: i.e. a pseudo-one step

procedure was used. The use of bis-MPA as ABx

monomer results in sterically hindered ester, which

is less reactive towards trans-esterification than the

other aliphatic esters, thereby decreasing the

amount of side reaction during the polymerization.

The use of a relatively low esterification tempera-

ture, 140 �C, also suppressed unwanted etherifi-cation and trans-esterification. Due to low

solubility of bis-MPA in most of the organic sol-

vents the synthesis (Fig. 1) was carried out by

heating the reactants without solvent, which re-

sulted in a melt. p-TSA was used as catalyst to

OH

OH

OH

OH

OH

N

O

O

O

O

O

OH

O

G1

-TSA

40 C

1.


increase the rate of the reaction. In its absence bis-

MPA is deposited in the cold areas of the reaction

vessel as sublimate, rather than reacting with the

substrate, which results in erratic branching. When

the reaction starts bis-MPA, slowly dissolves in the

polymer melt resulting first a thick dispersion ofthe solid in the melt, which becomes a clear liquid

when all bis-MPA is dissolved. The viscosity of the

reaction mixture increases with the progress of the

reaction.

3.2. Characterization of hyperbranched polyesters

The structure of polyester contains three dif-ferent units, dendritic, linear and terminal. In or-

der to distinguish between these differently

incorporated repeating units, model compounds

1–3, having low molar mass but resembling these

building blocks were synthesized. The chemical

shifts observed in 13C{1H} NMR spectra of these

model compounds were used for the assignment of

signals observed in the 13C spectra of polyesters.The pattern of signals in 13C{1H} NMR spectra of

the five generations, G1–G5, is similar. The

Fig. 1. (a) 13C{1H} NMR spectrum of polyesters G1 and

(b) 13C{1H} NMR spectrum of polyesters G4.

13C{1H} NMR spectrum of G4 polyester (DMSO-

d6) exhibits four distinct groups of signals (Fig. 1).

The methylene signals are around d 63–70 ppm

and the quaternary carbon atoms at d 42–52 ppm.

Methyl carbon signals appear at 20 ppm while the

carbon atoms of carbonyl around d 170–180 ppm.The quaternary carbon atom signals are found to

be least overlapping compared to those of other

carbon atoms and most sensitive to the groups

attached to them. Therefore they can be used to

diagnose the different type of repeating units that

differ distinctly in the degree of substitution.

The build-up of the hyperbranched polyester

was monitored by studying 13C{1H} NMR ofaliquots of reaction mixture taken out intermit-

tently. At the outset of reaction, in quaternary

carbon region only one signal at d 49.6 ppm cor-

responding to the quaternary carbon of bis-MPA

was visible. In the spectrum of first generation

polyester as the reaction proceeded, a signal was

observed at d 50.7 ppm due to quaternary carbon of

dendritic unit and signal at d 49.6 ppm was absent(Fig. 1(a)). Small aliquots from the reaction mix-

ture of G2 taken out at 60, 90, 180 and 260 min were

subjected to 13C{1H} NMR studies. Six signals

were observed in the quaternary region for all

aliquots as shown in Fig. 2 for 260 min one. This

Fig. 2. 13C{1H} NMR spectrum of reaction mixture of G2

polyester taken out after 260 min.

Fe C ¼ 0.0519A+0.0075 R2 ¼ 0:9995Pb C ¼ 0.0320A)0.0046 R2 ¼ 0:9998Cd C ¼ 0.1782A)0.0075 R2 ¼ 0:9972Zn C ¼ 0.2571A)0.0165 R2 ¼ 0:9991Cu C ¼ 0.0790A)0.0175 R2 ¼ 0:9996Ni C ¼ 0.0451A)0.0010 R2 ¼ 0:9997Co C ¼ 0.1075A)0.0270 R2 ¼ 0:9965


suggests that during initial stages of the reaction the

hyperbranched polyester contained not only the

branched, linear and terminal repeating units but

each of them also existed as focal point attached to

an acid group. After 5 h the 13C{1H} NMR re-

corded had only three signals at 50.4, 48.4 and 46.4corresponding to quaternary carbon atoms of ter-

minal, linear and branched unit respectively. Simi-

lar changes in 13C{1H} NMR spectra were noticed

during the progress of G3, G4 and G5 formation.

In quantitative 13C-NMR of each generation,

the area under the different quaternary carbon

resonance signals reveals the relative fractions of

the repeating units, which is called the degree ofbranching (DB) found to be 100%, 92.0% and 80%

for the first, second and third generation respec-

tively. The high DB values upto third generation

suggest that the pseudo-one-step synthesis in-

creases the probability of reaction of the monomer

unit with the hyperbranched skeleton. The degree

of branching for the fourth and the fifth genera-

tion found to be 51.5 and 50.0 respectively, seemsto be almost independent of the stoichiometric

ratio between the core molecule and the repeating

unit. The size exclusion chromatography was used

to characterize these hyperbranched polyesters by

molecular weight. The results are given in Table 1.

The SEC measurements are made in relation to

linear polystyrene standards using THF as solvent.

Since SEC depends on the radius of gyration, thebranched structures appear to exhibit lower mo-

lecular weight than the true one. Thus experi-

mentally determined Mn and Mw values for higher

generations may differ more from the theoretical

values as they are calculated with respect to linear

polystyrene standards. The polydispersity indices,

as shown in Table 1, indicate a narrow distribution

of hydrodynamic radius.

Table 1

Molecular weight distribution of hyperbranched polyesters

Polyesters Theoretical molecular weight (g/mol) M

�Mw

G2 1194 1

G3 2586 2

G4 5370 5

G5 10,938 11,

3.3. Calibration curves for metal ions

For the determination of metal ions using

FAAS, various parameters (viz. wavelength, slit

width, lamp current etc.) were set at optimum le-vel. The linear ranges for measurement under op-

timum conditions have been found to be 0.2–5.0,

1.0–10.0, 0.5–2.0, 1.0–15.0, 0.1–1.0, 1–10.0 and

1.0–10.0 lgml�1 for Cu, Co, Cd, Pb, Zn, Fe and

Ni, respectively. The linear equations along with

regression (R2) for each metal ion are as follows.

where, A is peak height absorbance, C is concen-tration in lgml�1. All the statistical calculations

are based on the average of four readings for each

standard solution in the given range.

3.4. Metal extraction by hyperbranched polyesters

The concentration of metal bound to a polyes-

ter generation (Mb) is expressed by equation.

Mb ¼ Mo �Ma;

where, Mo is initial metal ion concentration in 50

ml of distilled water, which was equilibrated with

0.005 g of hyperbranched polyester and Ma is

concentration of metal in the filtrate. The extent

of binding (EOB), number of moles of ametal ion bound per mole of polyester, is

expressed as

olecular weights (g/mol) �Mw/ �Mn

�Mn

342 1245 1.07

638 1989 1.32

427 3912 1.38

810 7098 1.66


EOB ¼ Mb=Cd;

where, Cd is the total concentration of hyper-branched polyester in the aqueous solution in mol/

l at optimum pH. The EOB values of various

generations of hyperbranched polyester for the

metal ions in aqueous solution are given in Table 2.

The experiments were repeated four times to assess

the precision of the EOB measurements. The low

RSD values signify the EOB data are reproducible.

The degree of branching calculated through 13CNMR spectroscopy suggests that G2, G3, G4 and

G5 contain 12, 24, 48 and 96 terminal hydroxyl

groups respectively. Presuming that ester groups

remain dormant and only hydroxyl groups coor-

dinate EOB is expected to 6, 12, 24 and 48 if each

metal ion coordinates with two hydroxyl groups. If

four terminal hydroxyl groups are involved then

maximum EOB will be 3, 6, 12 and 24 for G2, G3,G4 and G5, respectively. The maximum EOB for

G2, G3, G4 and G5 generations when they bind

with Cu(II) are 4.5, 10.1, 18.0 and 26.0 metal ions

per hyperbranched molecule (Table 2). Thus it

appears that G2, G3, G4 and G5 generally involve

the ester groups as well as terminal hydroxyl

groups for binding with each metal ion. The

binding capacity of these polyesters for the sevenmetal ions is found to be significantly larger than

those of chelating oxygen ligands (like EDTA) and

macrocycles (like crown ethers), which typically

bind with only one metal ion per molecule of the

ligand. The hyperbranched polyesters are found

fully effective for extraction of the seven metal ion

at 10 ngml�1 concentration level. At further lower

concentration levels extraction efficiency decreasesrapidly. The EOB values for the seven metal ions

Table 2

The EOB of G2, G3, G4 and G5 for the metal ions

Metal ion Efficiency of binding

G2 RSD (%) G3 RSD (%) G4

Cu(II) 4.5 2.8 10.1 1.2 18.0

Fe(III) 4.0 3.2 9.0 1.4 18.0

Pb(II) 3.5 4.5 8.0 3.2 16.0

Co(II) 2.4 4.6 7.0 1.0 15.6

Ni(II) 2.0 4.6 4.0 3.3 10.9

Cd(II) 2.0 4.7 7.0 1.6 14.0

Zn(II) 0.6 5.9 1.7 4.8 4.5

of Boltorn H30 (molecular weight 3570) were de-

termined and are compared with those of the

present hyperbranched polyesters (Table 2). The

values are somewhat higher than those of G3

(theoretical molecular weight 2586) but muchlower than that of G4. Thus it appears that metal-

extraction capability of present hyperbranched

polyesters is better than that of Boltorn ones.

3.4.1. Effect of pH

The effect of pH on the metal sorption capacity

was also studied to gain insight into relationship

between EOB (metal loading on the hyper-branched polyester) and protonation of the ligat-

ing sites. It was observed that for each metal ion,

the effect of pH followed the same trend for all the

generations. For example Fig. 3 shows it for

Cu(II). The optimum pH range for the maximum

loading was found to be 5.0–7.0 for Cu(II) and Pb,

4.5–7.0 for Fe(III), 6.0–8.0 for Co(II) and Ni(II),

6.0–7.5 for Cd(II) and 6.5–8.0 for Zn(II). Theprofile of efficiency of binding of G4 for all the

metal ions as a function of pH is shown in Fig. 4.

The EOB is very low at pH < 4:5, due to the de-

crease in the number of available oxygen binding

sites as they might get protonated. The difference

in EOB values for the various metal ions arises

probably due to their sizes, degree of hydration

and binding constant of their complexes formedwith the functionalities of the polyester.

3.4.2. Kinetics of sorption

The effect of equilibration time on the efficiency

of binding of the metal ions was studied.

The recommended procedure as mentioned in the

RSD (%) G5 RSD (%) Boltorn H30 RSD (%)

1.2 26.1 1.0 10.8 2.5

0.7 25.0 1.0 9.4 3.8

1.5 20.0 1.1 9.1 2.9

1.7 22.4 1.0 7.8 3.1

0.9 21.2 1.1 5.4 1.9

2.5 22.5 0.9 8.3 2.7

2.8 6.8 1.7 2.3 2.0

0

5

10

15

20

25

30

0 2 4 6 8 10 12pH of Cu (II) solution

EO

B

G2

G3

G4

G5

Fig. 3. Effect of pH on the sorption of Cu(II) for G2, G3, G4

and G5.

0

5

10

15

20

25

30

35

40

2 3 4 5 6

Generation

Equ

ilibr

atio

n tim

e re

quire

d fo

r ac

heiv

ing

max

imum

EO

B

Fe

Cu

Pb

Co, Ni

Zn

Cd

Fig. 5. Kinetics of metal ion sorption on G2, G3, G4 and G5.

5

10

15

20

25

30

EO

B o

f Cu(

II)

G2

G3

G4

G5


experimental section was applied using different

equilibration time. It was observed that the time

required to achieve the maximum EOB followedthe order G2 < G3 < G4 < G5 for all metal ions

(Fig. 5). This suggests that as we move on to

higher generation the complexity in the structure

increases and the coordination sites are so oriented

that their equilibration with the metal ions takes

longer time. The profile of EOB with equilibration

time is shown in Fig. 6 for all the seven metal ions.

The time required to achieve maximum EOB wasminimum for Fe(III), while it was maximum was

for Cd(II) as expected on the basis of the nature of

these Lewis acids.

0

5

10

15

20

25

30

0 2 4 6 8 10

pH of aqueous solution

EO

B

P b(II)

Cu(II)

F e(III)

Cd(II)

Co (II)

Z n(II)

Ni(II)

Fig. 4. Effect of pH on the sorption of Cd(II), Fe(III), Co(II),

Zn(II), Cu(II), Pb(II) and Zn(II) for G4.

0

0 10 20 30 40

Equilibriation time (min)

Fig. 6. Kinetics of Cu(II) sorption on various generation.

4. Conclusion

The new nitrogen centered hyperbranched

polyesters are synthesized upto fifth generation.

The degree of branching for fifth generation is50%. The new hyperbranched polyesters is found

promising for sorption of Cu(II), Ni(II), Cd(II),

Zn(II), Pb(II), Fe(III) and Co(II) at pH 4.5–8.0.

The EOB was found to be maximum for Cu(II)

(26.1) and minimum for Zn(II) (0.6). For all the

metal ions (concentration levels upto 10 ngml�1)


the hyperbranched polyesters were found efficient

extractants.

Acknowledgements

Authors thank CSIR (India) for financial

assistance.

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Hyperbranched polyester having nitrogen core: synthesis and applications as metal ion extractant

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